SDN and NFV is the next phase of technology change which will help service provider to launch the services in single click. This is all about the programmability of the networks by using open source software defined network controller.

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Saturday, October 3, 2009

In previous post of HSRP, a problem has highlighted of reverse and forwarding traffic when customer use the HSRP in LAN. This post is highlighting the problems when HSRP runs in PE-CE wan. Below is the diagram shown for reference purpose.

Customer R6 is connected with two PE routers for high availability. R3 is the active router with priority 255 and R2 is the standby router with priority 200. R1 ie receiving the lan routes from R2 as well as from R3 but selecting R2 as the best path because of smallest router-id assuming the cost of the both links in cloud is same. So the forwarding from R6 is happening via R3 router and reverse traffic is coming via R2. Which Problems Could Come 1.The different reverse and forwarding could cause problems ofin customers applications if applications are jitter or latency senstive.2. If the primary and backup path has different bandwidth allocation, In that case backup could be obstructed at anytime.

How to overcome the problem1.Change the IGP path cost which may bring other difficulties.2.Change the router id.

Apart from these remedies I am seeking another solution which could solve the current problem. If anyone is having anyidea , please share.

Hi,I think i have a way to make this happen. Most people may not like this though. you can use NAT (either a different NAT pool per CE or NAT overload on each CE) this will force the PE to send traffic back to that same CE. so if HSRP fails to the standby, the NEW NAT address will be used and the PE will equally send traffic back to the right CE over the right link. making the routing to be symetrical. My 5 cents